1. Field of the Invention
The present invention relates to a radio base station, user terminal and frequency band sharing method for sharing at least part of a frequency band between radio communication systems whose communication areas spatially and at least partially overlap each other.
2. Description of the Related Art
In recent years, studies are being carried out on a system configuration in which in a communication area of MCS (Macro Cell System) which is an existing radio communication system, a communication area of CRS (Cognitive Radio System) different from the MCS is arranged so as to overlap with the communication area of the MCS. In such a system configuration of communication areas of a plurality of radio communication systems overlapping with each other, it is under study how to improve utilization efficiency of frequency bands by sharing at least part of a frequency band among the plurality of radio communication systems.
When communication areas of a plurality of radio communication systems sharing a frequency band overlap each other, if a user terminal of a first radio communication system (e.g., MCS) is located near a radio base station of a second radio communication system (e.g., CRS), the user terminal receives considerable interference from the radio base station. Therefore, studies are also being carried out on the possibility of the user terminal of the first radio communication system (e.g., MCS) requesting the radio base station of the second radio communication system (e.g., CRS) to perform interference reduction processing based on a detection result of a broadcast signal (e.g., busy tone) from the radio base station (e.g., see Japanese Patent Application Laid-Open No. 2011-004002).
However, when communication areas of a plurality of radio communication systems sharing a frequency band overlap each other, as described above, if the user terminal of the first radio communication system (e.g., MCS) implements functions for enabling to detect a broadcast signal from the radio base station of the second radio communication system (e.g., CRS) and request the radio base station to perform interference reduction processing, there is a problem that the implementing load of the user terminal of the first radio communication system increases.